A semiconductor device may include a lower dielectric layer on a substrate, data storage patterns on the lower dielectric layer and spaced apart from each other in first and second directions, a cell dielectric layer on the lower dielectric layer and on the data storage patterns, voids in the cell dielectric layer and between ones of the data storage patterns, upper conductive contacts respectively on the data storage patterns and spaced apart from each other in the first and second directions, and upper conductive lines on the upper conductive contacts and spaced apart from each other in the second direction and extending in the first direction. Each of the upper conductive lines may be electrically connected to respective ones of the upper conductive contacts. The respective ones of the upper conductive contacts may be spaced apart from each other in the first direction.